1. Field of the Invention
The present invention relates to a multiple color image forming apparatus and method wherein a multicolor image is formed on a substrate using a liquid developer.
2. Discussion of the Background
Image forming methods using a liquid developer, such as an electro-photographic recording method and an electrostatic recording method, have certain advantages that a dry toner developing apparatus cannot achieve. In particular, because the liquid developer contains fine toner particles of a sub-micron size dispersed in a carrier solvent, methods using liquid developers can accomplish high image quality. Also, because the liquid developer image forming methods can obtain a sufficient image density using even a small amount of toner particles, they are economical and can accomplish a fine texture equivalent to that of printing, such as offset printing.
Various electro-photographic recording methods for forming a multiple color image are known.
A first known method uses four latent image retaining bodies, and simultaneously performs formation of latent images on respective latent image retaining bodies and development of each of the latent images for these latent image retaining bodies, and thereafter transfers sequentially developed visible images to a transfer body to form a superposed multicolor image on the transfer body.
A second known method uses only one latent image retaining body, and performs image formation by forming a latent image, developing the latent image, and transferring the developed image to a transfer body. The steps are sequentially repeated for each of several color images and a superposed multicolor image is formed on the transfer body.
A third known method uses serial sets of latent image formation and development devices to form serially stacked color images onto one latent image retaining body, whereby stacked multiple color image laminates defining a multiple color visible image are formed on the surface of the latent image retaining body and collectively transferred to a transfer body. This method, called the xe2x80x9cImage on Image Process (IOI process),xe2x80x9d is preferable from the standpoint of achieving a reduction in the size of the apparatus and precision of color superposition.
Nevertheless, the IOI process has a disadvantage caused by a peel off of a part of the toner particles of one color developed on a latent image retaining body from the latent image retaining body at a next color development station. The peel off may cause a degradation of image quality.
An object of the present invention is to provide a multiple color image forming apparatus and method in which peel off of toner particles of a previous color image from a latent image retaining body is suppressed, whereby a stable fine texture may be obtained.
Accordingly, according to a first aspect of the present invention, there is provided a multiple color image forming apparatus including a latent image retaining body, a first developing device, and a second developing device. The first developing device faces the latent image retaining body at a first developing station and is configured to develop a first latent image on the latent image retaining body using a first color liquid developer. The first color liquid developer contains a first solvent and first toner particles. The second developing device faces the latent image retaining body at a second developing station. The latent image retaining body at the second developing station retains a second latent image and supports a first color image developed by the first developing device. The second liquid developing device is configured to develop the second latent image using a second color liquid developer, and a reversible electrophoretic transfer efficiency of the toner particles of the first color image in the second liquid developer is 60% or less.
According to a second aspect of the present invention, there is provided a multiple color image forming apparatus including a latent image retaining body, a first developing device, a second developing device, and means for adjusting reversible electrophoretic transfer efficiency. The first developing device faces the latent image retaining body at a first developing station and is configured to develop a first latent image on the latent image retaining body using a first liquid developer. The first liquid developer contains a solvent and toner particles. The second developing device faces the latent image retaining body at a second developing station, and the latent image retaining body at the second developing station retains a second latent image and supports a first color image developed by the first developing device. The second developing device is configured to develop the second latent image using a second liquid developer. The reversible electrophoretic transfer efficiency of the toner particles of the first color image in the second liquid developer is set to be 60% or less by the means for adjusting.
According to a third aspect of the present invention, there is provided a multiple color image forming method including steps of forming a latent image on a latent image retaining body, which supports a first color image, and developing the latent image using a liquid developer. The first color image includes toner particles that have reversible electrophoretic transfer efficiency of 60% or less in the liquid developer.